Use constant-time circular timetable arithmetic

[A-BenLi06]

Summary

Replace iterative circular clamp/difference normalization with constant-time floor-mod arithmetic.

Problem

The existing helpers repeatedly add or subtract one period until a value reaches the requested window. Runtime is O(abs(offset) / period), so very large timetable offsets or persisted timestamps can monopolize the simulation thread. Extreme long values can also overflow while the loop is normalizing.

Change

• Normalize integral values with Math.floorMod.
• Normalize floating-point values with a floor-mod helper.
• Preserve the existing half-period tie direction.
• Reject non-positive periods instead of entering a non-terminating loop.
• Preserve NaN propagation for doubles.
• Add equivalence tests against the previous iterative semantics over representative ranges plus Long.MIN_VALUE/Long.MAX_VALUE cases.

Runtime becomes O(1) for all finite input magnitudes.

Validation

• ./gradlew test --no-daemon
• Full suite passed (113 tests).

Part of #32.